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 Post subject: Field iD
PostPosted: Sat May 02, 2015 8:04 pm 
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Location: N Dakota
Found my lost boulder by the river, I assume it has garnet scattered through it. The base rock is grey to black but saturated with bright gold mica wich turns coppery. It has some quartz crystal mixed in with clear cherry colored crystals. Most seem splintered or shattered but form irregular columns or cubes. And some cluster in groups. None are any larger than a pencil eraser by themselves. They appear to be brittle. Without any instruments except a magnifying glass what are my steps to verify this crystal? Color, translucence, structure. Then what? This was found on the Missouri River in N Dakota. It could be washed in from the west. It could be pushed in from glacial drift so it may not be "local" or it may be eroded out of the hillside. So I guess what I'm asking is what steps do you follow for field ID when you find any gem/ crystal. Dan

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 Post subject: Re: Field iD
PostPosted: Sat May 02, 2015 9:18 pm 
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I can't think of any in particular for garnet. That's probably because garnet is so distinctive--its typical dodecahedral shape is very uncommon and hard to mistake. Once you've seen a few you'll have trouble mistaking a crystal for anything else. In ND it really could be from anywhere--we found a beautiful piece of garnet schist with dime-sized garnets in a field in northern Montana last summer, all part of the glacial till (and no more in the immediate area).
But let's be honest here--what you have is definitely garnet. I can't say that for sure, of course, but I am pretty sure nevertheless. It sounds like it's in schist, and there aren't that many options.

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 Post subject: Re: Field iD
PostPosted: Sat May 02, 2015 11:17 pm 
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Kind of what I figured. More to the point of what I think I was looking for. What are the steps you take on a prospecting discovery to ID what you find. If it comes from a mine you have a pretty good idea of what is produced from that area. In this case I found it taking a break from the boat and fishing. So yes I stumbled on a 200 lb rock full of I'm not sure what! Once I start buying my tools it will be easier. A loop would be great! Don't have it yet. That is what I'm after. Even if I think your right! Dan

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 Post subject: Re: Field iD
PostPosted: Sun May 03, 2015 12:48 am 
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Hi Dan,

are they clean crystals? do you have a photo?

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 Post subject: Re: Field iD
PostPosted: Sun May 03, 2015 9:05 am 
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having issues with getting my photos here. its just me, I argue constantly with this computer refusing to do what I want it to. I should fire it for insubordination and general bad attitude.
The bits of crystal I have broken off are quite clear. 1 piece I looked at this morning was about 2mm thick x 7mm wide disc. I could see the tweezers through it. Depending on the light it varies in color a bit. Outside it really pops but indoors not so much. I would say pomegranate to cherry in color. Doesn't seem to have the structure I have seen with garnet in my gold pan, and its not very stable. crumbly. If i rub 2 pieces of the rock together it crushes into sand and the crystals do the same. It tends to run in small veins mixed with very soft black mica and quartz through the rock which changes from a grey black slate to grey green crumbly layers.
From what I see, color and clarity, perhaps a pyrope garnet. Small pieces break down into roughly cubes, larger pieces its hard to tell. Maybe tabular layers but no definite geometric outline other than straight lines and smooth glassy look.
Going to run a couple of pieces by the cutting disc and see if I can remove some larger sections of the crystal from the rock without destroying it completely. Then I will go back to war with the pictures and see if I can get something to post. Dan

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 Post subject: Re: Field iD
PostPosted: Sun May 03, 2015 9:23 am 
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reading through Barbra's Garnet group description Rhodolite? may be another idea.

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 Post subject: Re: Field iD
PostPosted: Sun May 03, 2015 11:33 am 
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You may also find some useful information here:
http://geophysics.ou.edu/geol1114/notes ... et_rx.html

Also, if you have issues getting photos on the forum, send them to me and I'll help you out with that.
bav@gemologyonline.com


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 Post subject: Re: Field iD
PostPosted: Sun May 03, 2015 2:29 pm 
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Thanks Barbra, I just signed up with imageshack this morning, will get a chance to try it out this week some time. Elbow surgery Tuesday, should have a few days to tinker after that. I will check out the links as well. Dan & Sally

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 Post subject: Re: Field iD
PostPosted: Sun May 03, 2015 2:40 pm 
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The gneiss photo was spot on to a piece I found a couple weeks ago in a farmers rock pile. The rocks I'm looking at now appear more like the schist but the crystals aren't well defined. I'll work on the pics and post later then you can all see!
Dan

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 Post subject: Re: Field iD
PostPosted: Sun May 03, 2015 5:38 pm 
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I like that geophysics link, that's pretty handy!

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 Post subject: Re: Field iD
PostPosted: Sun May 03, 2015 11:36 pm 
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Here are a couple of pics of the specimens from Dan&Sally:
Image
Image


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 Post subject: Re: Field iD
PostPosted: Tue May 12, 2015 10:41 pm 
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Disappointment, the garnet is highly fractured. Ran several pieces through the wet saw and nothing solid. might make good sandpaper. Working through the larger blocks now with a chisel in hopes of finding a hidden crystal not fractured. I have similar issues here with Knife river flint being fractured. -60 deg F in the winters will fracture most anything, but its the freezing and thawing that does most of the damage. Maybe I can find another use for garnet dust? Next

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 Post subject: Re: Field iD
PostPosted: Sat Jun 13, 2015 8:50 pm 
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Found another rock of the same material and structure except this has the small round garnets im used to finding in my gold pan. probably 10 miles from where I found the one in the pictures. Im now more confused than ever with whats in the first rock. Colors match, base rock too , but the xtal structure is so different in the first one. I can crush my latest find with a hammer and the little rounded Garnets just roll out. I can crush the crystals in the first rock into tiny pieces with my fingers, very brittle. So my field ID mystery goes on. August is coming soon and with it a release of funds to buy the equipment I need. I cant wait!

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